Optical network

ABSTRACT

An optical interconnection network in which more than one communication canccur at any give time is disclosed. The interconnection network can form part of a parallel computer, a fiber optic switching network, a massive video or data server or an asynchronous transfer mode (ATM) network. The network includes transmission network elements, reception network elements and a holographic storage element. The holographic storage element is located equidistant form all the transmission and reception network elements and stores therein a multiplicity of holograms. Each volume hologram is responsive to a different angle of incidence of wavelength. Each transmission network element includes a light directing unit which selectively provides at least one light beam of at least one desired angle of incidence to the holographic storage element, which, in turn, redirects each light beam towards a corresponding one of the reception network elements in accordance with the one of the volume holograms responsive to the corresponding angle of incidence.

FIELD OF THE INVENTION

The present invention relates to interconnection networks in general andto holographic interconnection networks in particular. The presentinvention also relates to parallel computers having such holographicinterconnection networks therein.

BACKGROUND OF THE INVENTION

The features which make electronics a wonderful medium for performingcomputations also make electronics a poor choice for massive highperformance communication networks between and within computers. Despitethis, a large number of parallel computer architectures, based onelectronics, have been proposed and many have been built. They aresummarized in the book by G. Lerman and L. Rudolph, Parallel Evolutionof Parallel Processors, Plenum Press, New York, 1993, which book isincorporated herein by reference.

Currently, most of the commercial parallel supercomputers consist of amultiplicity of high performance processors which communicate via amulti-stage interconnection network. Each processor communicates withthe interconnection network via its own specially designedprocessor-network interface.

The individual processors execute operations in excess of 100 millioninstructions per second (MIPS), have a local memory in excess of 64Mbytes and can transmit messages at a rate of tens of Mbytes/second.Modern parallel supercomputers, such as the CM-5 manufactured byThinking Machines Inc. of Cambridge, Mass., USA, the SP-1 manufacturedby International Business Machines Inc. of the USA, the CS-2manufactured by Meiko of England, the Paragon manufactured by IntelCorporation of the USA and the T3D manufactured by Cray ResearchCorporation of Maynard, Minn., provide the programmer with the abilityto send a message between any pair of processors even if a direct linkdoes not exist between the two processors. Each processor is typicallyknown as a "node".

Since electronic interconnection networks cannot support fullinterconnectivity (i.e. each processor being directly connected to everyother processor), they typically resort to multistaged networks, asdescribed in the book by G. Almasi and A. Gottlieb, Highly ParallelComputing, Benjamin-Cummings, 1989, which book is incorporated herein byreference. Unfortunately, in many communication patterns, there are notenough links and therefore, a plurality of messages must use the samecommunication links. Since at most one message may traverse a link atany time, serious performance degradations can ensue. Moreover, thelatency (i.e. the time needed for a message to traverse theinterconnection network) increases with the size of the network. At thepresent time, electronic networks appear to be limited to 500 nodes.

As a result of these drawbacks, optical interconnection networks,supporting thousands of nodes, have been proposed. Some mimic themultistage networks of electronic interconnection networks and, althoughthe optical networks may be faster, they have the same limitations asthe electronic ones. Others try to mimic a bus interconnectionarrangement; however, this arrangement does not scale easily. Stillothers route the signals through the network via a central device which,when it is modifying one connection, cannot be utilized for any othertask. Finally, there are schemes based on bulk optics which requireprecise alignment of the optics. Almost all of the designs are on paperonly and none of them are appropriate for massively parallel processingin which there are 10,000 or more processors. Furthermore, all of theprior art designs suffer from indeterminant transnission times.

SUMMARY OF THE PRESENT INVENTION

It is, therefore, an object of the present invention to provide anoptical interconnection network in which more than one communication canoccur at any given time. Accordingly, the interconnection network has acentralized holographic storage element in which are stored amultiplicity of volume holograms. The interconnection network can formpart of a massively parallel computer. The interconnection networkalternatively can form part of a fiber optic switching network, amassive video or data server or an asynchronous transfer mode (ATM)network.

In accordance with one preferred embodiment of the present invention,the optical interconnection network includes a multiplicity of networkelements arranged in a geometric arrangement, such as a sphere, and aholographic storage element centrally located within the geometricarrangement. The structure ensures that the network elements are allequidistant from the holographic storage element.

The holographic storage element has stored therein one volume hologram,responsive to a particular angle of incidence, per communication linkbetween a transmission and a reception network element. Eachtransmission network element includes a light directing unit and eachreception network element includes a light receiving unit. The lightdirecting unit selectively provides a light beam at a desired incidenceangle, where, due to the sensitivity of the volume holograms, thedesired incidence angle defines the output angle towards the desiredreception network element. The light receiving unit receives beams fromthe holographic storage elements and ensures that only one of the beamsis considered at any time.

There is therefore provided, in accordance with a preferred embodimentof the present invention, an optical interconnection network having afirst multiplicity of interconnections. The network includestransmission network elements, reception network elements and aholographic storage element located between the transmission andreception network elements. The holographic storage element storesvolume holograms, wherein each volume hologram corresponds to one of theinterconnections between one of the transmission network elements andone of the reception network elements. The transmission network elementscommunicate with the reception network elements by illuminating theholographic storage element with light at desired position and angles ofincidence corresponding to desired reception network elements thereby toactivate the corresponding volume hologram. Additionally, in accordancewith a preferred embodiment of the present invention, the lightdirecting unit includes a spatial light modulator formed of amultiplicity of selectable modulator elements, at least one for eachreception network element with which communication is desired. Themodulator elements can be activated individually or a set of modulatorelements can be activated. In the latter case, the result can becommunication with many reception network elements or it can be with asingle reception network element which requires many copies of the samemessage.

Moreover, in accordance with a preferred embodiment of the presentinvention, each of the reception network elements comprises a lightdetecting unit for detecting and receiving light from the holographicstorage element and for enabling a predetermined number ofcommunications to occur. The light detecting unit can be formed of asingle light detector which enables only a single communication at atime, or it can be formed of a matrix of detector elements. In thelatter case, the light detecting unit additionally includes apre-processor which, when a communication is initiated by activating atleast one detector element, disables all non-activated detectorelements. The light detecting unit can also be capable of receiving aset of light beams from one transmission network element at one time.

Finally, the network preferably includes a calibration unit locatable atpositions symmetrically across from a desired reception network elementfor use in implanting the volume holograms corresponding to the desiredreception network element.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic illustration of a holographic interconnectionnetwork,constructed and operative in accordance with a preferredembodiment of the present invention;

FIG. 2 is a schematic illustration of elements of the interconnectionnetwork of FIG. 1;

FIGS. 3A and 3B are schematic illustrations of two alternative detectorunits forming part of the interconnection network of FIG. 2;

FIG. 4A is a schematic illustration of an alternative embodiment of anetwork element forming part of the interconnection network of FIG. 2;

FIG. 4B is a schematic illustration of an alternative format of theinterconnection network of FIG. 2;

FIG. 5 is a schematic illustration of apparatus for calibrating aholographic storage element forming part of the interconnection networkof FIG. 2;

FIG. 6 is a schematic illustration of a wavelength division multiplexer(WDM) utilizing the holographic interconnection network of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIGS. 1 and 2 which illustrate a holographicinterconnection network 10, constructed and operative in accordance witha preferred embodiment of the present invention. It is noted that, inthe drawings, optical connections are indicated by dashed lines andnon-optical connections are indicated by solid lines.

The interconnection network 10 typically comprises a multiplicity ofnetwork elements 12 arranged in a geometric arrangement, such as asphere 16. The network elements communicate with each other via aholographic storage element 14 centrally located within the sphere 16.For parallel computers, each network element 12 would be connected toone processing unit of the computer.

The holographic storage element 14 stores volume holograms therein.Typically, the number of volume holograms stored is equal to the numberof interconnections between network elements which are desired. Forexample, if there are N network elements and it is desired that eachnetwork element speak with all of the others, then there are N² volumeholograms stored in storage element 14.

As is discussed in the book by R. J. Collier et al Optical Holography,Academic Press, 1971, which book is incorporated herein by reference,volume holograms respond uniquely to light at a specific angles ofincidence (i.e. illumination at one angle of incidence will be bentalong only one optical path). Light at differing wavelengths will alsohave the same effect. The present invention will be described withrespect to angles of incidence, it being appreciated that a similarnetwork responding to wavelengths is also within the purview of thepresent invention.

Due to this specificity, many uncoupled optical paths can be definedwithin the holographic storage element 14 and illumination of one path(at a specific angle or a specific wavelength) will not generateillumination along any other path. Thus, many network elements 12 cancommunicate through holographic storage element 14 at one time and theangle of incidence of a light beam defines the desired interconnection.

The network elements 12 communicate with each other by transmittingincoming light beams at a given angle to the holographic storage element14. The storage element 14 in turn, redirects each light beam to itsdestination network element 12, in accordance with the volume hologramwhich responds to the angle of the incoming light beam. For example, inorder to send a message from a first network element, labeled 12a, to asecond network element, labeled 12b, the first network element 12aprovides an incoming light beam 30, to be called herein a "source lightbeam", at an angle corresponding to the second network element 12b. Whenilluminated with the source light beam 30 at the selected angle ofincidence, the volume hologram corresponding to the interconnection fromnetwork element 12a to network element 12b is activated. This volumehologram bends the source light beam 30 into a "destination" light beam32 directed towards the destination network element 12b. Thus, thedestination of a message is defined by the angle of illumination of theholographic storage element 14.

FIG. 2 illustrates the conversations of three network elements 12a, 12band 12c, all of which occur at the same time. Network element 12a sendsa message to element 12b, network element 12b sends a message to element12c and network element 12c sends a message to element 12a. The sourcebeams are labeled 30a, 30b and 30c and are respectively produced bynetwork elements 12a, 12b and 12c. The corresponding destination beamsare labeled 32a, 32b and 32c. Because the communications are through theholographic storage element which has a different volume hologram perinterconnection and because the source beams 32a, 32b and 32c aremutually incoherent, all three communications can occur at the sametime, as described hereinabove.

It is noted that the path from a first network element to a secondnetwork element is not the same as the path from the second networkelement to the first. Thus, each interconnection is a one-waycommunication path.

Since all network elements 12 are on the sphere 16, they are equidistantfrom holographic storage element 14. Since all communication is throughthe holographic storage element 14, all light beams, both source anddestination, have optical paths of equal lengths. It is noted that thenetwork elements 12 can be placed around any geometric arrangement thatensures that all of the light beams have optical paths of equal lengths.The remaining description will utilize the sphere; it being recognizedthat this is by way of example only.

In the embodiment of FIG. 2, each network element 12 comprises an nodecontroller 20, a spatial light modulator and detector unit 22, amodulated light source 24 of temporally modulated light, and apre-processor 26. The modulated light source 24 produces light which istemporally modulated with data to be transmitted.

The spatial light modulator and detector unit 22 comprises a modulatormatrix 34 of spatial light modulator elements 23 for providing sourcelight beams 30 and a detector matrix 36 of detector elements 28 forreceiving destination light beams 32.

The modulator matrix 34 is lit by the temporally modulated light fromlight source 24. If the interconnection network of the present inventionis implemented in a parallel computer, the light source 24 is typicallyformed of a laser having a frequency which is suitable for theholographic storage element 14 and a modulating element for temporallymodulating the light emitted by the laser. If the holographic storageelement is formed of Lithium Niobate doped with iron (LiNbO₃ :Fe), adiode pumped double YANG laser providing green light, is appropriate.

As can be seen in FIG. 2, each network element 12 and, therefore, eachunit 22 is at a different location on the sphere 16 (FIG. 1). Inaddition, each spatial light modulating element 23 of each unit 22 is ata slightly different angle to the holographic storage element 14.Therefore, each element 23 corresponds to and enables communication witha different network element 12.

It is noted that the elements 23 can be any appropriate type of spatiallight modulating elements known in the art. They can be operated suchthat only one element 23 is active at once or such that a predeterminednumber can be active at once. In the latter case, the same message isprovided to many destination network elements.

It is further noted that each detector element 28 is located at aslightly different angle to the holographic storage element 14.Therefore, each detector element 28 defines a different angle for thedestination light beams 32.

The node controller 20 typically controls unit 22, activating thespatial light modulating element 23 which corresponds to the desireddestination network element 12. For the example of network elements 12aand 12b communicating, element 23b is activated. The network element 12autilizes the selected pixel 23b to emit light beam 30a.

As mentioned hereinabove, the holographic storage element 14 bends lightbeam 30a into light beam 32b. Beam 32b impinges upon detector element28a of the unit 22 corresponding to network element 12b, whereindetector element 28a corresponds to network element 12a. The detectorelement 28a is typically a photodetector. Each detector 28 provides amodulated signal to the preprocessor 26 when a light beam impinges uponit. It is noted that the pre-processor 26 can be separate from orintegral with the detector matrix 34.

Pre-processor 26 can operate in many different ways. Typically, itensures that, at any one time, only one detector element 28 is active.Alternatively, the pre-processor 26 can enable a predetermined number ofdetector elements 28.

If the interconnection network of the present invention is implementedinto a parallel computer, the pre-processor 26 also converts themodulated signal provided by the active detector element 28 into aformat, typically digital, which the processor connected to the networkelement 12 understands. To prevent many communications from occurring atonce, as soon as one detector element 28 becomes active, thepre-processor 26 disables all the other detector elements 28 for theduration of the communication.

It will be appreciated that any network element 12 can, at the sametime, send a message to one processor and receive a message from anotherprocessor. Alternatively, a sending processor can provide the samemessage to a plurality of processors by activating a plurality ofmodulating elements 23 at one time.

The detector matrix 36 can be implemented in a number of ways, all ofwhich must ensure that a predetermined number of communications areenabled at any one time. It can be formed of a single detector element28. The holographic storage element 14 is designed to direct beams fromany sending network element 12 to the single detector element 28. Itwill be appreciated that, in this embodiment, the information regardingwhich network element 12 initiated the communication must be in themessage being sent.

However, this embodiment requires that no two light beams impinge on thesingle detector element at the same time. Hardware arbitration circuitrycan be used to avoid simultaneous transmissions.

The detector matrix 36 can alternatively be implemented as a matrix ofdetector elements 28, as generally illustrated in FIG. 2 and detailed inFIGS. 3A and 3B to which reference is now made. In the embodiment ofFIG. 3A, the detector matrix 36 is a two-dimensional matrix of detectorelements 28, one per interconnection, with output pins 40a per columnand 40b per row. Matrix 36 also includes column and row selectioncircuitry 41 and 42, respectively, for selecting a column or row forreading. Initially, column selection circuitry 41 is operative andcontinually scans the column output pins 40b. Since only a few detectorelements 28 are likely to be active at any one time, most of the columnswill have no activity on them (equivalent to a logical "0"). FIG.3Ashows two active detector elements 28a and 28b.

The row and column selection circuits 41 and 42 are typicallyimplemented to perform a "winner-takes-all" circuit such that, as soonas it is determined that a detector element 28, such as 28a, is active,the output of the remaining detector elements 28 are disabled. In thisembodiment, only one communication at a time is allowed.

A further alternative embodiment is illustrated in FIG. 3B. In thisembodiment, the detector matrix 36 is much smaller and can beimplemented as a linear array 45 or as a matrix. In this embodiment, thesending network element 12 sends multiple copies, for example three, ofits message to the destination network element 12. Each sending networkelement 12 has its own combination of detector elements 28 to which itsends, through the holographic storage element 14. For example, a firstnetwork element 12 might send to the detector elements labeled 1, 3 and6 (illustrated with solid lines) and a second might send to detectorelements 6, 8 and 10 (illustrated with dashed lines).

In the embodiment of FIG. 3B, if one of the copies of the message iscorrupted, since another message was sent to that detector element 28 atthe same time, one or more of the other copies of the message will notbe corrupted at the same time. This is because no two network elements12 activate exactly the same detector elements 28. If the first networkelement 12 is currently sending a message, it has activated detectorelements 1, 3 and 6. The detector array 45 disables all elements but 1,3 and 6. When the second network element 12 begins sending, it willattempt to activate detector elements 6, 8 and 10. Since detectors 8 and11 are already disabled, they will have no effect. But the communicationwith detector element 6, when the first network element 12 is alreadycommunicating with detector element 6, will cause the output of detectorelement 6 to be corrupted. An output circuitry (not shown) which detectscorrupted signals ignores the output of detector element 6 and onlyutilizes the output of detector elements 1 and 3. Since the output ofdetector elements 1 and 3 are identical, only one of them is reallyneeded to ensure that the message is properly sent.

In a further embodiment, a dual-rail implementation is utilized in whichthere are two detector arrays 45, one (labeled 45a) for receivinglogical "1"s and one (labeled 45b) for receiving logical "0"s. Eachnetwork element 12 sends to the same set of detector elements in eachdetector array 45. Thus, the first network element 12 sends to detectorelements 1, 3 and 6 of each detector array 45, depending on the logicalvalue of the data being transmitted.

It is noted that the detector matrix 36 and spatial light modulatormatrix 34 do not have to be implemented into the single unit 22 shown inFIG. 2. Reference is now briefly made to FIGS. 4A and 4B whichillustrate two embodiments of a network element 12 which separate thedetector and spatial light modulator matrices 36 and 34, respectively.Similar elements are indicated with similar reference numerals.

FIG. 4A is a simplified illustration of one network element whichcomprises the node controller 20, light source 24, and pre-processor 26as described hereinabove. The spatial light modulator (SLM) matrix 34and detector matrix 36 are separated and the light which theyrespectively emit and receive are processed by a beam splitter 46. Beamsplitter 46 passes the outgoing light beams from the spatial lightmodulator matrix 34 and bends the incoming light beams towards thedetector matrix 36. It is noted that matrices 34 and 36 are located soas to ensure that the source light paths from the spatial lightmodulator matrix 34 to the holographic storage element 14 are of anequivalent length to the destination light paths back to the detectormatrix 36.

FIG. 4B is a schematic representation of an interconnection network inwhich at least some of the spatial light modulator matrices 34 of thedifferent network elements 12 are combined together into a single unit47 and at least some of the detector matrices 36 are combined togetherinto a single unit 48. Each network element 12 still comprises its ownlight source 24 and node controller (NC) 20; however, the pre-processors26 can either be separate, or combined into a single pre-processor 49,as shown. Each light source 24 is operative only for its correspondingspatial light modulator matrix 34.

Since the units 47 and 48 are large compared to the individual matrices,the units 47 and 48 may have to be curved so as to maintain the matrices34 and 36, respectively, along the surface of sphere 16 (FIG. 1). Sinceonly the matrices 34 and 36 operate with light beams (noted by dashedlines), the remaining communication being performed via electronicconnections (noted by solid lines), only matrices 34 and 36 have to beplaced on the surface of the sphere 16. The remaining elements, such asthe node controllers 20, can be placed elsewhere, as noted in FIG. 4B.It is noted that each node controller 20 still communicates with itscorresponding spatial light modulator matrix 34 and detector matrix 36.

Reference is now made to FIG. 5 which illustrates a system by which thevolume holograms are created within the holographic storage element 14,which is typically formed of a crystal, such as one made of LithiumNiobate doped with iron (LiNbO₃ :Fe). The system shown in FIG. 5 istypically operative with the embodiment of the network elements 12 shownin FIG. 4A.

To create a hologram in a crystal, two light beams must be shone on thecrystal, one from the input direction and one along the symmetricreflection of the desired output direction. Once the hologram is"fixed", as will be described later, light from the input direction willcause light to go out the output direction.

The network elements 12 are typically placed at their locations on thesphere 16 (FIG. 1) and the holographic storage element 14 is placed inits location concentric to the center of sphere 16. To create theoptical path from a network element, labeled 12d, to a network element,labeled 12c, (i.e. illumination from network element 12d will cause thelight to bend towards network element 12c), a phase conjugate mirror 50is placed directly opposite network element 12c, in order to create alight beam 56 headed in the output direction toward network element 12c.

Both network elements 12d and 12c emit light, through their respectiveunits 22, towards the holographic storage element 14. The emitted lightbeams are labeled 52 and 54. Some of light beam 54 from network element12c will pass the holographic storage element 14 and impinge upon mirror50 which will return it, as light beam 56, towards network element 12c.Since the light beam 54 is of low intensity and therefore, not intenseenough to implant the holographic information, mirror 50 is a phaseconjugate mirror which produces beam 56 which is typically more intensethan impinging beam 54. The beam 56, in conjunction with the lessintense input beam 52, is intense enough to create the relevant volumehologram. It is noted that the reference beam 52 and beam 56 must becoherent.

Mirror 50 remains in its location for the creation of all of the opticalpaths towards network element 12c. This involves consecutivelyactivating the light sources 24 and appropriate spatial light modulatorelements 23 of each network element 12. Afterwards, mirror 50 moves to alocation opposite another network element 12 and the process repeated.Once all of the volume holograms have been created, the holographicstorage element 14 is treated, in accordance with known treatments, soas to fix the holograms therein.

It will be appreciated that the holographic interconnection network ofthe present invention can be utilized anywhere where opticalinterconnections are desired and where it is desired to have manycommunications occurring at the same time. Reference is now made to FIG.6 which illustrates a wavelength division multiplexer (WDM) whichutilizes the holographic interconnection network of the presentinvention. In effect, in this embodiment, the holographicinterconnection network acts as a big switchboard for a fiber opticnetwork.

WDMs convert the wavelengths of light signals carried on fiber opticwaveguides 60. Each fiber optic waveguide 60 carries on it manydifferent channels of signals, each channel being defined by a differentwavelength. Thus, the fiber optic waveguide 60 may carry the channelsdenoted by λ_(i), λ_(j) and λ_(q). The WDM is operative to convert thewavelengths from one wavelength to another one, as desired. By changingwavelengths, the signal being carried is switched from one channel toanother.

In accordance with this alternative embodiment of the present invention,the holographic interconnection network is utilized to direct thesignals from one channel to another one. The transmitting side comprisesa filtering unit 62, comprising a plurality of filters each attuned tothe wavelength of one channel, to separate the signals into theirseparate channels. For each channel, the transmitting side alsocomprises a transmission unit is 64 comprising the transmission elementsof a network element 12. Each transmission unit 64 comprises an nodecontroller 20 and a spatial light modulator matrix 34 located on thesurface of the sphere 16 at whose center is located the holographicstorage element 14. On the receiving side are a plurality of wavelengthchanging apparatus 74, one for each outgoing channel or wavelength λ.

As in the previous embodiment, the node controller 20 activates thematrix element of modulator matrix 34 which corresponds to the desireddestination. The activated matrix element emits a light beam, forexample beam 66, having its corresponding wavelength λ_(q) at anincidence angle corresponding with the desired output wavelength. Theholographic storage element 14 redirects the source light beams,regardless of their wavelengths, in accordance with their incidenceangle. The redirected beam is received by the appropriate wavelengthchanging apparatus 74 which, in turn, produces a corresponding outputsignal with the desired wavelength.

Each wavelength changing apparatus 74 typically comprises a detector 76and a new channel creator 78. The detector 76 is similar to the detectormatrix 36 of the previous embodiment in that it detects the incidence oflight upon it and ensures that only one communication occurs at any onetime. Furthermore, detector 76 demodulates the data temporally modulatedin the light beam and thus, produces a data signal representing the datacarried by the light beam. Detector 76 can be formed of many detectorelements or just one, as described hereinabove.

Creator 78 includes therein a laser at the desired outgoing wavelength.Upon receipt of the data signal, creator 78 modulates the output of itslaser in accordance with the data signal. The result is a modulatedsignal with the desired outgoing wavelength, or, in other words, on thedesired channel.

FIG. 6 illustrates the conversion of the three source light beams havingwavelengths λ_(i), λ_(j) and λ_(q) into two outgoing light beams havingwavelengths λ_(j) and λ_(i). Each source light beam is processed by itsown transmission unit 64 and illuminates the holographic storage element14 at the angle defining the desired output wavelength. The beams havingwavelengths λ_(i) and λ_(q) are redirected to wavelength changingapparatus 74a and the beam having wavelength λ_(j) is redirected towavelength changing apparatus 74b. Typically, if two beams fall on adetector 76, the earliest one will be processed. Therefore, the nodecontrollers 20 have to be coordinated so as to ensure that each sourcebeam is directed to an available wavelength changing apparatus 74. Thisis especially true if the WDM is to act as a switchboard.

It will be appreciated by persons skilled in the art that theholographic interconnection network of the present invention has anumber of features. A network element can transmit, at once, the samemessage to a desired number of destination network elements. This"multi-casting" occurs whenever the spatial light modulator matrix 34activates more than one spatial light modulator element 23 at one time.

Due to the sensitivity of the holographic storage element 14, amultiplicity of communications can occur at the same time betweendifferent network elements. These communications are independent of eachother and therefore, do not require centralized coordination in order tooccur. Since the communications are independent, the failure of one nodewill not cause the entire network to fail.

Finally, it will be appreciated that, since all of the network elementsare similar, network elements can be added or removed as desired.

It will be appreciated that the holographic interconnection networks ofthe present invention can be implemented in any device which requiresmany interconnections between operating devices. For example, theholographic interconnection network can form part of a massivelyparallel computer. Alternatively, it can form part of a network of videoor data servers. Furthermore, it can be utilized as the interconnectionunit for asynchronous transfer mode (ATM) networks.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined by the claims which follow:

We claim:
 1. An optical interconnection network comprising:a firstmultiplicity of transmission network elements formed into a firstplurality of transmission units; a second multiplicity of receptionnetwork elements formed into a second plurality of reception units; anda holographic storage element located equidistant from all of saidtransmission and reception network elements and storing therein a thirdmultiplicity of volume holograms, each responsive to a different angleof incidence and each associated with a different interconnectionbetween one of said transmission network elements and one of saidreception network elements; wherein each of said transmission unitscomprises a light directing unit for selectively providing at least onelight beam, through at least one transmission network element, at leastone desired angle of incidence to said holographic storage element, andwherein said holographic storage element redirects each of said at leastone light beam towards a corresponding one of said reception networkelements in accordance with the one of said volume holograms responsiveto the corresponding angle of incidence.
 2. An optical interconnectionnetwork according to claim 1 and wherein said light directing unitcomprises a spatial light modulator comprising a multiplicity ofselectable modulator elements, one for each reception network elementwith which communication is desired.
 3. An optical interconnectionnetwork according to claim 1 and wherein each of said reception unitscomprises a light detecting unit for detecting and receiving light fromsaid holographic storage element and for enabling a predetermined numberof communications to occur.
 4. An optical interconnection networkaccording to claim 3 and wherein said light detecting unit comprises asingle light detector and enables only a single communication at a time.5. An optical interconnection network according to claim 3 and whereinsaid light detecting unit comprises one detector element for eachtransmission network element with which communication is desired and apre-processor for, when a communication is initiated by activating atleast one detector element, for disabling all non-activated detectorelements.
 6. An optical interconnection network according to claim 3 andwherein said light detecting unit comprises a matrix of detectorelements, a column selector and a row selector, wherein said columnselector continually scans columns of said array and said row selectorputs out signals from said detector elements of a column only once saidcolumn selector receives an indication of light reception on at leastone of the detector elements in said column.
 7. An opticalinterconnection network according to claim 3 and wherein said lightdetecting unit comprises an array of detector elements, said array beingcapable of receiving a set of light beams from one transmission networkelement at one time.
 8. An optical interconnection network according toclaim 1 wherein said light directing unit comprises a spatial lightmodulator comprising a multiplicity of selectable modulator elements,wherein a predetermined number of said modulator elements correspond toeach reception network element with which communication is desired,wherein each of said reception network elements comprises a lightdetecting unit for detecting and receiving light from said predeterminednumber of spatial light modulator elements through said holographicstorage element and for enabling corresponding communications to occur.9. An optical interconnection network according to claim 1 andadditionally comprising a node controller for controlling said lightdirecting unit and for receiving output of said light directing unit.10. An optical interconnection network according to claim 9 and whereinsaid node controller activates more than one spatial light modulatingelement at a time.
 11. An optical interconnection network according toclaim 1 and additionally comprising a calibration unit locatable atpositions symmetrically across from a desired reception network elementfor use in implanting the volume holograms corresponding to said desiredreception network element.
 12. An optical interconnection network havinga first multiplicity of interconnections, the network comprising:asecond multiplicity of transmission network elements; a thirdmultiplicity of reception network elements; and a holographic storageelement located between said transmission and reception network elementsand storing therein a first multiplicity of volume holograms, whereineach volume hologram corresponds to one of said interconnections betweenone of said transmission network elements and one of said receptionnetwork elements, wherein said transmission network elements communicatewith said reception network elements by illuminating said holographicstorage element with light at desired angles of incidence correspondingto desired reception network elements thereby to activate thecorresponding volume hologram.
 13. A parallel computer comprising:amultiplicity of processors; and an optical interconnection networkoptically connecting said multiplicity of processors, wherein saidoptical interconnection network has a first multiplicity ofinterconnections and comprises:a second multiplicity of transmissionnetwork elements; a third multiplicity of reception network elements;and a holographic storage element located between said transmission andreception network elements and storing therein a first multiplicity ofvolume holograms, wherein each volume hologram corresponds to one ofsaid interconnections between one of said transmission network elementsand one of said reception network elements, wherein said transmissionnetwork elements communicate with said reception network elements byilluminating said holographic storage element with light at desiredangles of incidence corresponding to desired reception network elementsthereby to activate the corresponding volume hologram.
 14. A fiber opticswitching network comprising:a multiplicity of fiber optic cables; andan optical interconnection network optically connecting saidmultiplicity of fiber optic cables, wherein said optical interconnectionnetwork has a first multiplicity of interconnections and comprises:asecond multiplicity of transmission network elements; a thirdmultiplicity of reception network elements; and a holographic storageelement located between said transmission and reception network elementsand storing therein a first multiplicity of volume holograms, whereineach volume hologram corresponds to one of said interconnections betweenone of said transmission network elements and one of said receptionnetwork elements, wherein said transmission network elements communicatewith said reception network elements by illuminating said holographicstorage element with light at desired angles of incidence correspondingto desired reception network elements thereby to activate thecorresponding volume hologram.
 15. An optical interconnection networkfor connecting a multiplicity of video servers, the network comprising:afirst multiplicity of transmission network elements; a secondmultiplicity of reception network elements; and a holographic storageelement located equidistant from all of said transmission and receptionnetwork elements and storing therein a third multiplicity of volumeholograms, each responsive to a different angle of incidence and eachassociated with a different interconnection between one of saidtransmission network elements and one of said reception networkelements, wherein each of said transmission network elements comprises alight directing unit for selectively providing at least one light beamat least one desired angle of incidence to said holographic storageelement, and wherein said holographic storage element redirects each ofsaid at least one light beam towards a corresponding one of saidreception network elements in accordance with the one of said volumeholograms responsive to the corresponding angle of incidence.
 16. Anoptical interconnection network for connecting a multiplicity of dataservers, the network comprising:a first multiplicity of transmissionnetwork elements forming a first plurality of transmission units; asecond multiplicity of reception network elements forming a secondplurality of reception units; and a holographic storage element locatedequidistant from all of said transmission and reception network elementsand storing therein a third multiplicity of volume holograms, eachresponsive to a different angle of incidence, wherein each of saidtransmission units comprises a light directing unit for selectivelyproviding at least one light beam, through at least one transmissionnetwork element, at least one desired angle of incidence to saidholographic storage element, and wherein said holographic storageelement redirects each of said at least one light beam towards acorresponding one of said reception network elements in accordance withthe one of said volume holograms responsive to the corresponding angleof incidence.
 17. An optical asynchronous transfer mode (ATM)interconnection network, the network comprising:a first multiplicity oftransmission network elements forming a first plurality of transmissionunits; a second multiplicity of reception network elements forming asecond plurality of reception units; and a holographic storage elementlocated equidistant from all of said transmission and reception networkelements and storing therein a third multiplicity of volume holograms,each responsive to a different angle of incidence, wherein each of saidtransmission units comprises a light directing unit for selectivelyproviding at least one light beam, through at least one transmissionnetwork element, at least one desired angle of incidence to saidholographic storage element, andwherein said holographic storage elementredirects each of said at least one light beam towards a correspondingone of said reception network elements in accordance with the one ofsaid volume holograms responsive to the corresponding angle ofincidence.